The normal development of the immune system depends not only upon the proliferation of appropriately stimulated lymphocyte clones, but also upon the inactivation or deletion of autoreactive clones. The cellular mechanisms that determine whether a lymphocyte clone proliferates or is inactivated after engagement of the antigen receptor are not known, but may be of fundamental importance in understanding lymphoproliferative disorders including autoimmunity and malignant transformation. It is postulated that phosphomyristin C (PMC), a major cellular substrate of protein kinase C (PKC), along with PKC itself constitute a negative signalling pathway that leads to the growth arrest of B cells and thymocytes in response to antigen receptor cross-linking. The major goal of this proposal is to test the hypothesis that the expression of PMC in B cells and thymocytes confers a growth arrest phenotype upon these cell types. Additionally, the cellular and molecular biology of PMC expression will be explored. Two genetic tests of the hypothesis that PMC confers a growth arrest phenotype are proposed. First, PMC and PKC genes will be transferred into B cell lines to generate lines expressing elevated levels of both proteins. The response of these cell lines to receptor signalling will be studied to test their responsiveness to receptor signalling. Second, transgenic mice will be constructed that constitutively express elevated levels of PMC in the thymic and B cell compartments. The B and T cell compartments of these mice will be studied to determine if the transgene confers a growth arrest phenotype upon the recipient cells. The possibility that PMC plays an important role in the receptor-associated cell death of certain B cells will be directly tested at the cellular level by functional intervention with speciflc antibodies. Monoclonal antibodies against PMC will be transferred into intact cells in order to interfere with the function of PMC. Three aspects of the cellular and molecular biology of PMC will be investigated: 1) the expression and phosphorylation of PMC during the cell cycle. 2) the molecular basis for the dramatic induction of B cell PMC by cross-linking the antigen receptor, and 3) to identify, purify, and clone the proteins that associate with PMC.